The water temp gauge is more likely to work, unlike the fuel gauge it is a sealed system and as long as the seals are good it should work. The dye in the fluid may have disappeared making it hard to read. The solder joints connecting the tubing are a bit delicate and easy to lose the seal.
I had mine repaired for a modest cost by the “The Temperature Gauge Guy” several years ago but at the time he was hoping to retire and pass the business to someone else, I don’t know the current status.
The thermosylphon unit that controls the grille shutters on mid ’30’s was usually set to be fully open at 160 degrees. Engine temp will go above this on a hot day. The gauge on mine leaves it ambiguous, as it doesn’t read temp, just hot and cold.